This invention relates to novel substituted derivatives of 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid and analogs thereof which are useful for the treatment of hypertension. U.S. Pat. No. 4,141,899 to Arcari et al. issued Feb. 27, 1979, discloses 4,5,6,7-tetrahydroimidazo[4,5-c]pyridine derivatives as antiulcer and antisecretory agents. Further examples are disclosed in Arzneim. Forsch. 34 (11) 1467-1471 (1984). These compounds differ from the ones disclosed in this invention in that they lack a substituent group at the 6-position. This variation, in combination with substitution at other positions of the imidazo[4,5-c]pyridine ring provide novel compounds now found to have antihypertensive activity. Japanese Patent applications J5 9095-286A to Otsuka Seiyaku Kojy, published Jan. 6, 1984, discloses imidazo[4,5-c]pyridine 6-carboxylic acid derivatives having psycholeptic, hypotensive, central nervous system or analeptic activity.
A Belgian Patent No. 902,611 entitled "New Imidazo-Pyridine-6-Carboxamide Derivatives Useful as Antiviral Agents" discloses related compounds limited to an amide function in a C.sub.6 position of a nuclear structure having the positions numbered as shown in the formula as follows: ##STR1## Such compounds limited to the amide function are disclosed by Belgian Patent No. 902,611 as pharmaceutically active agents. Additionally related compounds having a carboxyl function at the C.sub.6 position are disclosed by the Belgian Patent No. 902,611 but only for use as intermediates.
Thus the compounds of the first three of the above references differ from those disclosed in this invention by virtue of bearing no substituent groups at N.sub.1, N.sub.3, N.sub.5, or C.sub.4 ; but carrying a spiro ring at C.sub.4. Further the present invention excludes compounds having a carboxylic acid group disclosed only as intermediates in Belgian Patent No. 902,611 discussed above. The present invention is thus pharmaceutical compositions having compounds of formula I' as defined hereinafter and a pharmaceutically acceptable carrier and method of use therefor. Such differences provide unobvious variance over the prior art.